Vertical- Lantern Galvanometer. 439 



a coil of covered copper wire, No. 11 of the American wire- 

 gauge, about 10 centimetres long and 6 in diameter, having 

 a resistance of 0*323 ohm. A small bar magnet, 5 centimetres 

 long and weighing six and a half grammes, gave, when introduced 

 into the coil, a deflection of 40°. On withdrawing the magnet 

 the needle moved 40° in the opposite direction. 



2. A small coil, 20 centimetres long and 3*5 in diameter, 

 made of No. 16 wire and having a resistance of 0*371 ohm, 

 through which the current of a Grenet battery, exposing 4 

 square inches of zinc surface, was passing, was introduced into 

 the centre of a large wire coil, whose resistance was 0*295 ohm, 

 connected with the galvanometer. The deflection produced was 

 20°. The same deflection was observed on making and break- 

 ing contact with the battery, the smaller coil remaining within 

 the larger. 



3. A coil of No. 14 copper wire, 60 centimetres in diameter, 

 and containing about 40 turns, the resistance of which was 0*85 

 ohm, was connected with the galvanometer, and placed on the 

 floor. Raising the south side 6 inches caused a deflection of 

 4°. Placing the coil with its plane vertical, a movement of 2 

 centimetres to the right or left caused a deflection of 3°, and of 

 20 centimetres of 10°. A rotation of 90° gave a deflection 

 of 12°, and one of 180° of 24°. These deflections were of 

 course due to currents generated by the earth's magnetism. 



4. Thermo- currents. — Two pieces of No. 22 wire, 15 centi- 

 metres long, were taken, the one of copper, the other of iron 

 wire, and united at one end by silver solder. On connecting 

 the other ends to the galvanometer, the heat of the hand caused 

 a deflection of the needle of 20°. 



5. A thermo-pile of 25 pairs, each of bismuth and antimony, 

 was connected to the instrument. The heat from the hand 

 placed at 5 centimetres distance caused a deflection of 3°. 



6. Two cubes of boiling water acted differentially on the pile. 

 At the distance of 5 centimetres the deflection was 20° ; moving 

 one to 10 centimetres, the deflection v/as reduced to 5°. 



7. Voltaic current. — A drop of water was placed on a zinc 

 plate. While one of the connecting copper wires touched the 

 zinc, the other w T as made to touch the water. The deflection 

 was 16°. 



The claim which is here made for the instrument, however, 

 is rather for the general principle of its construction than for 

 the advantages possessed by the individual galvanometer above 

 described, which was constructed at short notice, to meet an 

 emergency. The comparatively small cost for which it may be 

 fitted to the vertical lantern, the readiness with which it may be 

 brought into use, the brilliantly illuminated circle of light 



